He didn't. He died from a medication that was administered to MJ through an IV. A medicine that is used to knock people out while you do a short procedure (because it doesn't last long). Or it is used to keep people in a drug induced coma on a continous drip. A drip which is carefully monitored and titrated accordingly as needed. Someone had to keep giving it or it was left on. Basically, the MD was allowing the medicine to drip and LEFT it.

That medicine should NEVER be given outside a hospital setting. It is most certainly NOT a prescription medication.